1. Field of the Invention
The present invention relates to a video cassette recorder (hereinafter referred to as a VCR) designed to perform recording and reproduction of signals on tapes accommodated in two types of tape cassettes (hereinafter referred to as cassettes), having different sizes, by a head of a drum disposed midway in a tape path starting with a reel engaging a supply reel base and ending with a reel engaging a take-up reel base so that the tape can be wound therearound at a predetermined angle while it is moving from the supply reel to the take-up reel under a fixed tension.
2. Description of the Related Art
In a conventional VCR, recording or reproduction of signals is performed by a head of a drum disposed midway in a tape path starting with a reel engaging a supply reel base and ending with a reel engaging a take-up reel base so that the tape can be wound therearound at a predetermined angle while it is moving from the supply reel to the take-up reel under a fixed tension.
FIG. 1 is a perspective view of components of a structure for winding the tape under a fixed tension.
Reference numeral 106 denotes a tension post which is elastically brought into contact with a recording tape 30 forming a predetermined path for detecting the tension of the tape. A tension arm 114 for retaining the tension post 106 is supported in such a manner as to be pivotal about a shaft 114b at one end 114a thereof. The tension arm 114 is urged by a spring 115 counterclockwise so that it can elastically press against the tape 30. The tension of the recording tape 30 acts on the tension post in the form of a moment of force which rotates the tension arm 114 clockwise. After the tension arm 114 has shifted clockwise and the tape 30 thereby extends along a straight line, the moment of force applied to the tension arm 114 reduces even when the same amount of tension is applied to the tension arm 114. One end 116a of a band brake 116 is coupled to the tension arm 114. The other end 116b of the band brake 116 is fixed to a substrate of a device.
In the above-described structure, the band brake 116 can load an adequate braking torque on the rotation of a supply reel base 117.
More specifically, when the tension of the tape 30 is increased, the tension arm 114 shifts to the right, reducing the load on the band brake 116. Consequently, the resisting force of the supply reel base 117 to the tape 30 is reduced, reducing the tension of the tape 30. When the tension of the tape 30 is reduced, the tension arm shifts counterclockwise, increasing the load on the band brake 116. Consequently, the braking force of the supply reel base 117 which acts on the tape 30 increases, thus increasing the tension of the tape 30.
Tension control means arranged in the manner described above maintains the tension of the tape 30 to a fixed value by controlling the braking force applied to the tape 30 supplied from the supply reel base 117.
In recent years, there have been demands for reduction in the size of the apparatus and for increase in the recording time, and tapes employing cassettes having different sizes are available on the market.
Conventional VCRs employing cassettes having different sizes are mainly for business use. In order to apply a predetermined stable tension to the tape, such a VCR adopts an electric tension control means in place of a conventional mechanical tension control means.
However, in the electric tension control means, the reel must be driven by a direct motor dedicated to the use of the reel, thus increasing production cost.
In the mechanical tension control means, since the position of the reel is limited by the band brake serving as the control means, the reel and the tension control means must be moved together, making the device complicated.